A rationale on the role of intermediate Au(III)-vitamin C complexation in the production of gold nanoparticles

Preparation of gold nanoparticles, particularly gold nanorods, by wet chemistry processes involves gold seeds, an Au(III) salt, structure directing surfactants, and metal ion additives in the growth solution into which a weak reducing agent is added. The most commonly employed weak reducing agent is l-ascorbic acid (vitamin C) which is known to reduce many metal ions in the solution phase and form complexes with relatively low stability constants. A purple-gray gold-ascorbate compound, obtained from the reaction of sodium tetrachloroaurate(III) with sodium ascorbate, is now reported. The compound possesses the expected structural features of vitamin C-metal complexes as verified by its C-13 CP-MAS NMR spectrum. A discussion is also presented on the possibility of gold-ascorbate complexation operating in gold nanoparticle formation.